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In 1878, he secured the contract for the Caledonian Railway Bridge over the Clyde, and in 1882 he was awarded the reconstruction contract for the Tay Rail Bridge, which had collapsed in 1879. His company went on to construct the Forth Bridge which was completed in 1890. At the time, the Tay and Forth bridges were the largest of their type in the world. They were notable not just for their size but also the use of steel in the Forth Bridge, and the riveting method developed by Arrol to attach the girders to one another.

The bridge is, even today, regarded as an engineering marvel. It is 2.5 km (1.6 mi) in length, and the double track is elevated 46 m (approx. 150 ft) above high tide. It consists of two main spans of 1,710 ft (520 m), two side spans of 675 ft, 15 approach spans of 168 ft (51 m), and five of 25 ft (7.6 m). Each main span comprises two 680 ft (210 m) cantilever arms supporting a central 350 ft (110 m) span girder bridge. The three great four-tower cantilever structures are 340 ft (104 m) tall, each 70 ft (21 m) diameter foot resting on a separate foundation. The southern group of foundations had to be constructed as caissons under compressed air, to a depth of 90 ft (27 m). At its peak, approximately 4,600 workers were employed in its construction. Initially, it was recorded that 57 lives were lost; however, after extensive research by local historians, the figure has been revised upwards to 98.

Both bridges are known for their high safety factors, a natural result of the under-design of the first Tay bridge by Thomas Bouch, and both bridges have recently (2008) been renovated.

Other notable bridges followed, including: Tower Bridge in London, completed in 1894. Construction started in 1886 and took eight years with five major contractors Sir John Jackson (foundations), Baron Armstrong (hydraulics), William Webster, Sir H.H. Bartlett, and Sir William Arrol & Co.. It employed 432 construction workers. E W Crutwell was the resident engineer for the construction. Two massive piers, containing over 70,000 tons of concrete, were sunk into the river bed to support the construction. Over 11,000 tons of steel provided the framework for the towers and walkways. This was then clad in Cornishgranite and Portland stone, both to protect the underlying steelwork and to give the bridge a pleasing appearance.